We have already hinted on the diversity of networking. Many different systems have to talk to each other. And they have to speak the same language. They also have to understand the same language the same way.
People often think that body language is universal. But it is not. Back in my early teens, my father took me to Bulgaria. We were sitting at a table in a park in Sofia, when a vendor approached us trying to sell us some roasted almonds.
I had not learned much Bulgarian by then, so, instead of saying no, I shook my head from side to side, the “universal” body language for no. The vendor quickly started serving us some almonds.
I then remembered I had been told that in Bulgaria shaking your head sideways meant yes. Quickly, I started nodding my head up and down. The vendor noticed, took his almonds, and walked away. To an uninformed observer, I did not change the body language: I continued using the language of shaking and nodding my head. What changed was the meaning of the body language. At first, the vendor and I interpreted the same language as having completely different meaning. I had to adjust my own interpretation of that language so the vendor would understand.
It is the same with computers: The same symbols may have different, even outright opposite meaning. Therefore, for two computers to understand each other, they must not only agree on the same language, but on the same interpretation of the language.